[DOCS] Remove testenv annotations from doc snippet tests (#80023)

Removes `testenv` annotations and related code. These annotations originally let you skip x-pack snippet tests in the docs. However, that's no longer possible.

Relates to #79309, #31619

docs/reference/slm/apis/slm-api.asciidoc

@@ -1,5 +1,4 @@
 [role="xpack"]
-[testenv="basic"]
 [[snapshot-lifecycle-management-api]]
 == {slm-cap} APIs
 

docs/reference/slm/apis/slm-delete.asciidoc

@@ -1,5 +1,4 @@
 [role="xpack"]
-[testenv="basic"]
 [[slm-api-delete-policy]]
 === Delete snapshot lifecycle policy API
 ++++

docs/reference/slm/apis/slm-execute-retention.asciidoc

@@ -1,5 +1,4 @@
 [role="xpack"]
-[testenv="basic"]
 [[slm-api-execute-retention]]
 === Execute snapshot retention policy API
 ++++

docs/reference/slm/apis/slm-execute.asciidoc

@@ -1,5 +1,4 @@
 [role="xpack"]
-[testenv="basic"]
 [[slm-api-execute-lifecycle]]
 === Execute snapshot lifecycle policy API
 ++++

docs/reference/slm/apis/slm-get-status.asciidoc

@@ -1,5 +1,4 @@
 [role="xpack"]
-[testenv="basic"]
 [[slm-api-get-status]]
 === Get {slm} status API
 

docs/reference/slm/apis/slm-get.asciidoc

@@ -1,5 +1,4 @@
 [role="xpack"]
-[testenv="basic"]
 [[slm-api-get-policy]]
 === Get snapshot lifecycle policy API
 ++++

docs/reference/slm/apis/slm-start.asciidoc

@@ -1,5 +1,4 @@
 [role="xpack"]
-[testenv="basic"]
 [[slm-api-start]]
 === Start {slm} API
 

docs/reference/slm/apis/slm-stats.asciidoc

@@ -1,5 +1,4 @@
 [role="xpack"]
-[testenv="basic"]
 [[slm-api-get-stats]]
 === Get snapshot lifecycle stats API
 ++++

docs/reference/slm/apis/slm-stop.asciidoc

@@ -1,5 +1,4 @@
 [role="xpack"]
-[testenv="basic"]
 [[slm-api-stop]]
 === Stop {slm} API